1. Field of the Invention
The present invention relates to an optical disk reproducing apparatus and method, and more particularly, an optical disk reproducing apparatus and method having improved servo control.
2. Description of the Related Art
Generally, an optical disk player reproducing an optical disk in which digital data are written with an MPEG system is provided with, as shown in FIG. 1, a pick-up 3 detecting a signal recorded in the optical disk 1 by irradiating a laser beam through a light emitting laser diode, a sled motor 4 moving the pick-up 3 in a radial direction of the optical disk 1, a spindle motor 2 rotating the optical disk 1, a driver 6 driving the sled motor 4 and the spindle motor 2, an R/F unit 5 converting a signal detected from the pick-up 3 into a binary signal, a servo unit 7 controlling the driver 6 in accordance with a focus error signal FE, a tracking error signal TE, and a rotation speed of the optical disk 1, a digital signal processing unit 8 converting the binary signal into a digital data and then restoring the digital data which are compressed video/audio data, an MPEG decoder 9 decoding the compressed video/audio data for output, a microcomputer 11 controlling data flow in the optical disk player, and a memory 12 storing data temporarily therein.
With reference to FIG. 1, a method for detecting a signal written in the optical disk player will be described in detail.
The pick-up 3 continuously detects signals written in the tracks of optical disk 1 while the optical disk 1 is rotating, and the R/F unit 5 filters and shapes a high frequency signal detected by the pick-up 3 into a binary signal. The binary signal, which has only two levels, i.e., high and low state, is restored to the original digital data by the DSP 8, and the restored data is decoded into moving picture data by MPEG decoder 9. During reproduction, the servo 7 outputs a servo-control signal to the driver 6 to perform tracking and focusing. This servo control operation is performed in accordance with a tracking error signal and a focusing error signal that are obtained photoelectrically by a light receiving circuit, which includes a photodiode PD, in the pick-up 3.
The microcomputer 11 controls the servo 7 to perform the tracking or focusing operation of the pick-up 3, and controls the MPEG decoder 9 to generate output in accordance with the key commands requested from a user; whereby the moving picture data can be stably reproduced and searched.
In such an optical disk player, the tracking and focusing control are the important servo operations which determine the stability of the moving picture data output. Push-pull and a differential phase detection (DPD) servo control methods are generally adopted in the conventional art. Description will be made in detail with respect to the push-pull and the DPD methods, respectively.
FIGS. 2A and 2F illustrate the servo-control operation, particularly, the tracking operation according to the conventional art. In the push-pull method, as shown in FIG. 2A, a beam spot formed on a track of the disk 21 passes through an object lens 22 and is photoelectrically converted by a bipartite optical detector 23, in which a photodiode is divided into two parts. The photoelectrically converted electric signal is subtracted and amplified by a differential amplifier 24 and is outputted as a tracking error signal.
FIGS. 2B to 2E illustrate various tracking states of the beam spot as the beam spot moves in the track direction. Specifically, FIG. 2B illustrates that the beam spot moves in the track direction, but is slanted to the left. Here, the right side of the bipartite optical detector 23 detects the beam spot more brightly than the left side, whereby the tracking error signal has a positive (+) output. Accordingly, the servo 7 outputs a tracking control signal to move the beam spot to a center of the track. In FIG. 2C, the beam spot moves in the track direction and is placed in the center of track. The beam spot detected by the bipartite optical detector 23 has evenly distributed brightness so that the tracking control operation maintains the tracking error signal in the current state. FIG. 2D illustrates that the beam spot moves in the track direction, but is slanted to the right. Here, contrary to FIG. 2B, the left side of the bipartite optical detector 23 detects the beam spot more brightly than the right side, whereby the tracking error signal has a negative (xe2x88x92) output. Thus, the servo 7 outputs a corresponding tracking control signal to move the beam spot to the center of the track. Eventually, the servo 7 outputs the tracking control signal to move the beam spot to the center of the track, whereby the tracking error signal from the bipartite optical detector 23 becomes zero.
However, when the depth of the pits formed in the optical disk becomes xc2xc of a wavelength xcex of the laser beam, that is xc2xcxcex, although the beam spot is slanted to the right while moving in the track direction, the beam spot detected by the bipartite optical detector 23 may have symmetrically identical brightness as shown in FIG. 2E. Consequently, the tracking error signal, i.e., the output signal of the bipartite optical detector 23, becomes zero, so that it is mistakenly considered that no tracking correction is required, which leads to a tracking error.
FIG. 2F illustrates the DPD method in the conventional art, and the tracking-control operation according to the DPD method will now be described.
Electric signals received from an optical detector 30, which is quartered, are A, B, C and D, respectively. These signals are combined into (A+C)+(B+D) and (A+C)xe2x88x92(B+D), respectively, by amplifiers 31,32, and 33 and a differential amplifier 34. The signal (A+C)+(B+D) is applied to the R/F unit 5 and then outputted as a binary signal, while the signal (A+C)xe2x88x92(B+D), which is a tracking error signal, is applied to the servo 7 and used for tracking control.
FIGS. 2G-2I illustrate various tracking states of the beam spot as the beam spot moves in the track direction. As shown in FIG. 2G, the beam spot detected in the quartered optical detector 30 has symmetrically even brightness as in FIG. 2E. By differentially amplifying two electric signals, each signal being the sum of two signals from two diagonally positioned quarters of the of the quartered optical detectors 30, the tracking error signal (A+C)xe2x88x92(B+D) is negative (xe2x88x92). Tracking control, which moves the beam spot toward the center of the track, therefore, occurs. In FIG. 2H, the left and right sides of the tracking error signal have even light brightness, but in the diagonal direction the tracking error signal has different brightness, so that the tracking error signal (A+C)xe2x88x92(B+D) is negative (xe2x88x92). In FIG. 2I, the tracking error signal (A+C)xe2x88x92(B+D) is also negative (xe2x88x92), and thus tracking control is accomplished so that the beam spot moves to the center of the track, thereby resolving the problems with the push-pull method.
However, since both the conventional push-pull and DPD methods perform the servo-control operation using a single beam spot, there is a problem in that servo errors, that is tracking and focusing errors, occur when the disk has a defect such as stained blots or scratches on the track of the optical disk.
An object of the present invention is to provide a servo device and method for an optical disk using a plurality of beams that prevents a servo error caused by a defect on the optical disk.
These and other objects are achieved by providing an optical disk reproducing apparatus, comprising a pick-up forming at least a first beam spot on an optical disk, and receiving a reflection of said first beam spot; a servo signal generator generating first servo signals from said reflected first beam spot; a defect detector detecting defects in said optical disk; and a servo controller servo controlling said pick-up based on said first servo signals and output of said defect detector.
These and other objects are further achieved by providing an optical disk reproducing apparatus, comprising a pick-up forming a plurality of beam spots on an optical disk, and receiving reflections of said beam spots; a servo signal generator generating servo signals associated with and based on at least one of said reflected beam spots; and a servo controller selecting servo signals associated with one of said beam spots and servo controlling said pick-up based on said selected servo signals.
These and other objects are still further achieved by providing a method of servo controlling in an optical disk reproducing apparatus, comprising forming at least a first beam spot on an optical disk; receiving a reflection of said first beam spot; generating first servo signals from said reflected first beam spot; detecting defects in said optical disk; and servo controlling said pick-up based on said first servo signals currently generated by said generating step and output of said detecting step such that said servo control of said pick-up is based on said currently generated first signals when said detecting step does not detect a defect and said servo control is not performed based on said currently generated first servo signals when said detecting step detects a defect.
These and other objects are additionally achieved by providing a method of servo controlling in an optical disk reproducing apparatus, comprising forming a plurality of beam spots on an optical disk; receiving reflections of said beam spots; generating servo signals associated with and based on each of said reflected beam spots; and selecting servo signals associated with one of said beam spots; and servo controlling said pick-up based on said selected servo signals.